yes, any whie/gray item will work for runewords (if it has the correct number of sockets)
you can cube socket white items (will give random number of sockets)
or have larz socket a5 quest (for max sockets, limited by its ilvl)

just make sure your char meets the lvl reqs for all the runes in the runeword
hel rune lowers the str and dex reqs of the item by 15-20%

Elite armors and weapons have higher str/dex/level reqs, so the advantage of putting a runeword into one (for more damage for weapons, more defense for armors) must be significant enough to compensate it. Also, runewords have a level requirement of the highest of its runes and the base item. For example, anything with an Um zune will have a level req of at least 47 and anything involving a colossus blade will have one of at least 50.

Worth doing in elite items:
All melee weapon runewords involving one or more runes higher than let's say Lem.
The same with armor for melee characters.